Clozapine is the prototypical atypical antipsychotic drug and represents a tremendous improvement over conventional antipsychotics in terms of therapeutic efficacy and reduced side effect liability for the treatment of schizophrenia. Understanding the pharmacological properties that are important for clozapine's unique profile can help lead to the discovery of improved and safer antipsychotic drugs for the treatment of schizophrenia. One approach for investigating the molecular bases underlying the relationship of pharmacological agents and behavior has been the use of gene-targeted knockout or transgenic animals. This technique allows for the manipulation of receptors for which selective pharmacological ligands do not exist. One restriction of this approach is that most of the knockout mutations that have been developed are available only in mice - not rats. Therefore, it is necessary to have preclinical assays for mice in order to utilize these new and potentially powerful new techniques. The current proposal represents an important first step in this process. Two-lever drug discrimination is a valuable preclinical behavioral model that has been used to investigate the discriminative stimulus properties of clozapine in rats and has helped identify neurotransmitter receptor targets for putative atypical antipsychotics. Wild-type mice (C57BL/6J) will be trained to discriminate clozapine from vehicle and then a series of atypical and typical antipsychotic drugs will be tested to determine which drugs generalize to clozapine's discriminative cue. Establishing this procedure in wild-type mice will allow for the future use of knockout and transgenic mice and will expand the tools available to molecular geneticists and behavioral pharmacologists. This will help to increase our understanding of the perplexing pharmacology of schizophrenia.